A high speed printer of the type having a printing head movable in a direction perpendicular to the recording medium is known and is used, among other things, to permit different thickness of the recording medium. Usually, one or more than one spring is used to press the printing head into engagement against the recording medium. The drawback of this arrangement is that the printing head is continuously influenced by a force directing the head towards the recording medium, which, among other things, makes changing and feeding of recording paper more difficult. To overcome the above drawbacks it is also known to produce the pressing force by means of an electromagnet mounted on a carriage. In this arrangement, the deenergizing of the magnet results in the printing head being withdrawn from the recording medium. However, locating the electromagnet on the movable carriage, leads to two other drawbacks, i.e., the increased need of space and of serious import, the increase in weight of the movable mass thereby resulting in slower carriage movements, and consequently lower printing speed.
A feature of the present invention is to make it possible to control the printing head in a direction to or from the recording medium and at the same time to eliminate the drawbacks of the above-described known constructions. According to the teachings of the invention a construction has been developed whereby the printing motion relative to the carriage is determined by an expandable bladder or bellows acting upon the printing head, and said bladder or bellows being connected to a second bladder or bellows by means of an air hose. The second bladder or bellows is arranged in a fixed manner relative to the printer frame and has its compression determined by an electromagnet.
In the following description, the invention is explained in greater detail by way of example and with reference to the drawing, which in the sole figure shows diagrammatically a side view of a printing head and a control device for controlling the swinging motion of the printing head.